Method and apparatus for monitoring a system

ABSTRACT

A method for monitoring a system, in which a plurality of acoustic images are recorded and compared at defined intervals of time over a period of time extending several weeks. A large system can be monitored reliably and with little complexity if the acoustic images each contain a plurality of acoustic image areas which are arranged in a spatially different manner, and, between respective recordings of the image areas of an acoustic image, an acoustic sensor is aligned with an image area, which is to be recorded, of a next image area by being moved.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority, under 35 U.S.C. § 119, of Germanapplication DE 10 2008 023 863.5, filed May 16, 2008; the priorapplication is herewith incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a method for monitoring a system, in which aplurality of acoustic images are recorded and compared at definedintervals of time over a period of time extending several weeks.

Operators of large machines or systems incur high costs on account ofunforeseen damage to wearing parts, for example bearings, belts, etc. Ifthe defective parts are changed only after the defect has openly come tolight, this is associated with failure of the affected system during theintended operating time and thus with losses in the operationalthroughput. In order to avoid this, wearing parts can be changedregularly, optimum maintenance cycles being able to be defined only foruniform wear behavior. In practice, the wear behavior is not uniform,thus resulting in unnecessary changing of parts or failures despiteregular maintenance.

It is known practice to obtain statements on the state of wear fromacoustic signals. International patent disclosure WO 04/017038 A1presents a method in which a system is monitored with the aid of aportable directional microphone. Malfunctions within the system can bevisualized by diagnosing the noise emitted by the running system inorder to facilitate diagnosis for system maintenance. For this purpose,the directional microphone is aimed at the defective system and thefrequency spectrum of the noise of the defective system is compared witha previously recorded frequency spectrum of the system without a defect.The type and location of the defect can be inferred using correspondingevaluations.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a method and anapparatus for monitoring a system that overcome the above-mentioneddisadvantages of the prior art devices and methods of this general type,which method can also be used to monitor a large system with simplemeasures.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a method for monitoring a system. Themethod includes recording and comparing a plurality of acoustic imagesat defined intervals of time over a period of time extending severalweeks. The acoustic images each contain a plurality of acoustic imageareas which are disposed in a spatially different manner, and, betweenrespective recordings of the acoustic image areas of an acoustic image,an acoustic sensor is aligned with an image section, which is to berecorded, of a next image area by being moved.

The object is achieved by a method of the type mentioned at the outset,in which, according to the invention, the acoustic images each contain aplurality of acoustic image areas which are arranged in a spatiallydifferent manner, and, between respective recordings of the image areasof an acoustic image, an acoustic sensor is aligned with the imagesection, which is to be recorded, of the next image area by being moved.In particular, a large system with a multiplicity of system componentscan be monitored in this manner in an economically favorable andnevertheless reliable way using only a single acoustic sensor.

The system monitoring may be wear monitoring and/or defect monitoring.The method is particularly suitable for monitoring a system having arelatively large number of identical or similar functional units. Such asystem is, for example, a mail sorting system which may have a largenumber of identical compartments, for example up to 1,000 compartments.In such a system, the wear on individual functional units progressesover a relatively long period of time, with the result that there issufficient time for monitoring wear with measurements and evaluations.The spectra obtained from frequency analysis and/or amplitudedistribution, for example, change over the course of time as a result ofthe wear on the functional units. Comparing these spectra with empiricalvalues or spectra for a new system or a new functional unit can be usedto determine a degree of wear on the individual functional units, withthe result that decisions can be derived for service.

As a result of the automatable method according to the invention, thereis no need to use a plurality of separate acoustic sensors in a largesystem having a large number of functional units. The method can therebybe carried out in a favorable manner and can remain in the background—asfar as the apparatus complexity is concerned—such that the performanceof the tasks of the systems is not impaired.

When carrying out the method according to the invention, it issufficient to use only one single acoustic sensor to record all acousticimages. The acoustic sensor may be set up at a suitable distance fromthe system to be monitored and may be aimed at the system. The acousticimage containing acoustic data which are relevant to diagnosis—andpossibly also further data—can now be obtained by a scanning movement ofthe acoustic sensor, the acoustic sensor recording image area by imagearea. The image areas may be arranged in a predetermined manner withrespect to one another, with the result that the next orientation of themovement of the acoustic sensor between the recordings of the imageareas may likewise be predetermined. This makes it possible to scan aplurality of signal sources, in particular identical or similar signalsources, in succession.

In order to determine wear or a defect, the acoustic images areadvantageously recorded in an identical manner in order to achieve goodcomparability. The images can then be compared with one another. Forexample, a recorded image is compared with a previously recorded image,thus making it possible to determine the progress of wear or a defectfrom a change in the acoustic data. It is also possible to compare therecorded acoustic image with reference data which can be obtained, forexample, from a first recorded image of a new system or can beconcomitantly provided with the system or functional units. Images orimage areas can be compared by comparing acoustic parameters.

The acoustic images are spatially assigned acoustic characteristicswhich may be composed of the acoustic image areas. They are expedientlyrecorded in a predetermined rhythm, for example daily or weekly, inorder to be able to respectively currently determine current progress ofwear or a state of wear. The acoustic images can be compared with oneanother or with reference data by comparing an entire image with apreviously recorded entire image or by comparing only a section of theacoustic image with an expediently identical section of an earlier imageor corresponding reference data. An image area may be understood asmeaning an assignment of noise data to spatial coordinates, an imagearea being able to be a point image, a line image, a two-dimensionalimage or even a 3-dimensional image.

The acoustic sensor can be moved by moving the inherent acoustic sensorelement or an element of the sensor that guides sound waves to thesensor element.

The movement can be carried out in a particularly simple manner and withlittle outlay in terms of apparatus if the acoustic sensor is pivoted inorder to be aligned with the next image section. The sensor may remaintranslationally at one location and may be pivoted in one dimension, forexample, by a rotary drive in order to carry out a scanning movement inone line, for example. A rotary drive which allows pivoting in twodimensions is also conceivable, with the result that a plurality oflines can be scanned, for example.

The acoustic sensor may be intended to record airborne acoustic data,the sensor being aligned, during its movement, with a spatial area fromwhich a new acoustic image area is intended to be recorded. A movablestructure-borne sound sensor which acoustically measures an object viaan acoustic bridge is likewise possible. The acoustic bridge, forexample a steel spring, may be moved in a loop over the object or aplurality of objects and may make the acoustic recording in the process,the acoustic data being assigned, for example, to the coordinates of therespective support of the acoustic bridge and the acoustic image areathus being produced. Alternatively, the acoustic bridge may be set up ata location intended for it, for example, and may rest there while anacoustic measurement is being carried out. The bridge is then set up atanother location and a new acoustic measurement is started.

In the case of a large, elongate system, such as a mail sorting systemhaving a multiplicity of compartments, or in the case of a large rotarymachine which is expediently acoustically imaged from a plurality ofdirections, the acoustic sensor may be translationally shifted by atransport apparatus in order to be aligned with the next image section.Particularly suitable for this is movement on a rail, in particular on aceiling rail, from which the acoustic sensor can be suspended and can bemoved with little generation of noise. A combination of translationaland rotational movement of the acoustic sensor is particularlyadvantageous, thr sensor being able to record, for example, a firstnumber of acoustic image areas solely by being pivoted and recording afurther number of image areas following a translational movement, forexample along an elongate fan apparatus.

A high level of positioning accuracy when evaluating a degree of wearcan be achieved if the acoustic sensor is a directional microphone forrecording spatial image areas. The sound pressure data of the spatialimage areas can be separated from one another to a good extent, with theresult that adjacent noise does not distort an image area very much.

Another advantage of the method is that suitable programming makes itpossible to generate not only acoustic images with a rectangular outlinebut also any desired outlines of the acoustic images. An acoustic imagewhose outline corresponds to the outline of the system or to that areaof the system which contains the functional units to be monitored isexpediently generated. It is thus possible to avoid unnecessarymeasurements in systems with an outline which is not rectangular. Partsof the system which are not relevant to the measurements need not bescanned either. In this case, the outline of the system may be seen fromthe point of view of the acoustic sensor.

In another advantageous embodiment of the invention, acoustic imageareas are examined for a temporary influence. It may be the case thatthe image areas are distorted by temporary obstacles, for example anoperator. Such images which have been distorted by a temporary influenceshould be evaluated differently to image areas without the temporaryinfluence or should be excluded from an evaluation. A temporaryinfluence may be detected by sudden rough deviations from earlier imageareas of the same functional unit or of the same image section occurringin an image area. In this case, a plausibility check is advantageouslycarried out, which check examines a rough deviation in order todetermine whether it stems from wear or even a defect, for example amaterial fracture, or from a fault which cannot be taken into account,for example acoustic shadowing.

In a system having a multiplicity of functional units, it may be thecase that the functional units have been subjected to a different degreeof wear. In order to adapt the wear analysis to the current wear, it isadvantageous if a scanning rate of the image areas is different. Imageareas which image system parts which need to be monitored to a greaterextent since they have been subjected to a greater degree of wear, forexample, are generated more often than image areas of other systemparts. The scanning rate can be adapted, for example, to a risk of wear.

A different degree of wear on the individual functional units may arisein the case of a multiplicity of identical functional units in thesystem to be monitored. A greater degree of wear on a functional unit incomparison with other functional units can be detected if image areas ofan acoustic image are compared with one another.

Another embodiment variant of the invention proposes that the acousticsensor is fastened to a person, and image areas are recorded duringactivities performed by the person in order to operate the system. Inorder to record the image areas, the acoustic sensor may be brought veryclose to a functional unit to be monitored or may be inserted into thelatter without disturbing the person at work. Image areas and dataobtained from the latter may be stored in a memory worn by the person ormay be transmitted wirelessly, for example via WLAN, to a central dataprocessing unit, for example.

The recordings are advantageously synchronized on the basis of acharacteristic of the person. As a result, a time which is suitable fora recording can be determined by a process unit which can control therecording. The characteristic may be a location or an activity of theperson that is suitable for a recording. The location can be determinedby use of appropriate sensors and the activity can be determined, forexample, by effects of the activity which are detected.

The recording synchronization is expediently triggered by an input bythe person, which thereby controls the recording of an image area. Aparticularly favorable time for recording one or more image areas may beselected.

The recording synchronization may be triggered by the person operatingthe system, for example by acknowledging an activity, for example theacknowledgement that a compartment of a mail sorting system has beenemptied. As a result, a controlling process unit can detect that theperson is now very close to a functional unit as a result of carryingout the operation and there is thus a suitable moment for a recording.

In a mail sorting system, an image area is advantageously recorded whenthe person empties a sorting compartment, in particular while the personis reaching into the sorting compartment. An acoustic sensor which isfastened, for example, to the person's sleeve can thus be directlyinserted into a functional unit, with the result that a very goodacoustic image area can be obtained.

The acoustic image area can be obtained during a period of time, only atemporal section of the entire image area, for example, being used toevaluate the wear monitoring or defect monitoring, for example only sucha temporal section in which the acoustic sensor is inside a sortingcompartment by virtue of an operator. The recording may have alreadystarted beforehand by virtue of the recording synchronization, with theresult that a first part of the recording is not used for wear analysis.

The invention is also aimed at an apparatus for monitoring a system, theapparatus has an acoustic sensor and a process unit which is intended tocontrol the recording of a plurality of acoustic images and thecomparison of the images at defined intervals of time over a period oftime extending several weeks.

According to the invention, it is proposed that the apparatus contain amovement device for moving the acoustic sensor, and that the acousticimages each contain a plurality of acoustic image areas which arearranged in a spatially different manner, and that the process unit isintended to control a movement of the acoustic sensor between respectiverecordings of the image areas of an acoustic image such that theacoustic sensor is aligned with the image section, which is to berecorded, of the next image area.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a method and an apparatus for monitoring a system, it is neverthelessnot intended to be limited to the details shown, since variousmodifications and structural changes may be made therein withoutdeparting from the spirit of the invention and within the scope andrange of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is an illustration showing an apparatus for monitoring wear on amail sorting system according to the invention; and

FIG. 2 is a diagrammatic, perspective view of a section of the mailsorting system and microphones of the apparatus, one of which isfastened to an operator of the mail sorting system.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawing in detail and first,particularly, to FIG. 1 thereof, there is shown a diagrammaticallysimplified illustration of a system 2, for example a mail sortingsystem, which is monitored by a wear and/or defect monitoring apparatus4 for wear on functional units 6 and the mechanical elements of thelatter. The apparatus 4 which is likewise illustrated onlydiagrammatically in FIG. 1 includes an acoustic sensor 8 in the form ofa directional microphone which is connected to a motor-driven rotatingunit 10 having a vertical axis and to a motor-driven rotating unit 12having a horizontal axis. The rotating units 10,12 can pivot theacoustic sensor 8 in two dimensions about two shafts which areperpendicular to one another.

The apparatus 4 also contains an evaluation unit 14 for acoustic signalswhich are received by the acoustic sensor 8, a database 16 for acousticparameters and rotary transducer signals for the two rotating units 10,12, and a control unit 18 for the rotating units 10, 12, which controlunit is connected to a program unit 20 for the rotatable units 10, 12.An evaluation unit 22 is used to evaluate the acoustic parametersdetermined and to forward the evaluation results to an output unit 24for outputting data, for example information relating to repair andmaintenance work, maintenance intervals, elements to be replaced,affected functional units 6 and the like. The evaluation unit 22 hasaccess to a memory 26 for limit values of the acoustic parameters. Theunits 14 to 26 form a process unit 28 for controlling the monitoring ofwear.

The drives of the two rotating units 10, 12 are controlled by thecontrol unit 18 in such a manner that the entire system 2 can be scannedby moving the acoustic sensor 8 horizontally and vertically. The twodrives simultaneously have rotary transducer outputs, the output signalsfrom which are supplied to the database 16. The output of the acousticsensor 8 is connected to the evaluation unit 14 which determinesacoustic parameters of the system 2 which are then likewise supplied tothe database 16. The database 16 thus stores a multiplicity of acousticparameters of the system 2 to be monitored with their associatedcoordinates.

The evaluation unit 22 for the acoustic parameters determined obtainsthe limit values for the acoustic parameters from the memory 26 andcompares them with the acoustic parameters determined and the values ofthe latter. If the evaluation unit 22 determines that the permissiblelimit values have been exceeded, it signals a necessary repair ormaintenance measure via the output unit 24. The acoustic parameters maybe amplitudes or frequencies or the distribution thereof and maygenerally be generated from the recorded acoustic signal by mathematicalmethods.

In order to monitor wear and/or defects of the system 2, the latter issubdivided into a number of areas 30, 32, 34, 36. The areas 30, 32, 34may each be scanned by a single acoustic image area of the acousticsensor 8. The areas 36 are not scanned by the acoustic sensor 8 sincethe elements or functional units arranged there are not intended to bemonitored for wear. The acoustic image areas assigned to the areas 30,32, 34 produce an acoustic image of the system 2 in their entirety or insubgroups. In this case, the areas 30, 32, 34 are arranged in rows—fiverows in FIG. 1 by way of example—which can be scanned in succession bythe acoustic sensor 8 with one image area per area 30, 32, 34.

In this case, the areas 30, 32, 34 are assigned to different scanningrates since the functional units 6 contained in them have been subjectto a different degree of wear and can thus be assessed as more criticalor less critical in terms of wear. The hatched areas 32 are checked at afirst scanning rate, for example daily. The areas 34 with closerhatching are monitored at a higher scanning rate, that is to say in amore continuous manner in terms of time, for example every six seconds.The areas 30 which are not hatched are monitored at a lower scanningrate, for example weekly.

If evaluation of the acoustic data from the acoustic image areas revealsduring recording and comparison that serious deviations from previousimages occur in one or more image areas and these deviations areafflicted with attenuation or interfering noise which is not caused bywear, for example the pushing of a trolley past the system, those areas38 which are cross-hatched in FIG. 1 and the acoustic image areasthereof may be excluded from the evaluation. The evaluation unit 22 canmake a decision on this.

An acoustic image to be compared may contain one or more acoustic imageareas. In a first variant, the acoustic images or acoustic data of theacoustic images are compared with a previously recorded acoustic image.This may be a reference image which was recorded when the system 2 wasfirst operated or was new or which stems from a state of the system 2 orthe functional units of the latter which has been run in but iscompletely intact in the corresponding area 30, 32, 34. In this manner,an acoustic image which is afflicted with interference can be comparedwith an “intact” acoustic image. Comparison with acoustic parameterswhich are predefined ex works and may be contained in the memory 26 islikewise possible.

Comparison with a plurality of previous acoustic images is also possiblein order to detect a change profile of a parameter, for exampleamplitudes of chosen frequencies. In addition, comparison of a pluralityof image areas, which are recorded in real time, for example insuccession, in identical areas 30, 32, 34 is expedient. If, for example,a plurality of areas 34 which accommodate identical functional units 6are scanned in succession, these image areas which are recorded in realtime can be compared with one another. Evaluation of the image areas maybe aimed at detecting abnormalities of individual functional units 6 incomparison with other functional units 6 and thus detecting individualdefective or greatly worn functional units 6 from operational functionalunits 6.

Instead of the acoustic sensor 8, there may be a structure-borne soundsensor which acoustically measures vibrations which are transmitted fromthe areas 30, 32, 34 to a sensor means of the sensor via an acousticbridge. For this purpose, the sensor may be moved from area 30, 32, 34to area 30, 32, 34, the measurement taking place during the movement orbetween movements. In the case of measurement in a loop, for example,the acoustic bridge travels over the areas 30, 32, 34 on a path which isintended for it and is specially prepared for this purpose, for examplein that it is not varnished. Alternatively, each area 30, 32, 34 mayhave one or more—in particular prepared—locations at which the bridge isset up and rests there during a measurement. The sensor is accordinglymovable and can move or pivot.

Further possible ways of recording image areas are illustrated in FIG.2. FIG. 2 shows a section of the system 2, namely a number of sortingcompartments 40 in a sorting area of the system 2, which sorting areacontains a total of 200 of such sorting compartments 40. Each sortingcompartment 40 forms an area 34 which is recorded by an individualacoustic image area. Instead of the locally fastened acoustic sensor 8or in addition to the latter, an acoustic sensor 8 is provided and canbe pivoted by a rotating unit 12 and can be translationally shifted on arail 44 by a transport apparatus 42. The acoustic sensor 8 can thus bemoved along the 200 sorting compartments 40 and can be aligned with theindividual areas 30, 32, 34 in this manner.

Alternatively or additionally again, an acoustic sensor 46 is provided.This sensor is fastened to a sleeve 48 of a person 50, for example anoperator of the system 2. The operator empties the individual sortingcompartments 40 if required and reaches into them for this purpose inorder to remove items of mail which are stacked in them and to stackthem in a container 52.

Before a sorting compartment 40 is emptied in this manner, the person 50operates an acknowledgement button 54 by which the process unit 28 knowswhich sorting compartment 40 the person 50 is now beginning to empty.Operating the acknowledgement button 54 is a recording synchronizationwhich is simultaneously an operation by the person 50, by which theprocess unit of the system 2 knows that the corresponding sortingcompartment 40 is now being emptied and will then be available again forfurther stacking of items of mail.

Acoustic recording of the acoustic sensor 46 may begin after theacknowledgement button 54 has been operated and may be continued over afixed period, for example. During this period, the person 50 reachesinto the sorting compartment 40 and removes the items of mail stackedtherein. In this case, the acoustic sensor 46 enters the interior of thesorting compartment 40 and can thus record the noise inside the sortingcompartment 40 in a manner which is essentially undisturbed by ambientnoise. From this relatively long recording, the process unit 28 mayselect a time range, for example in which particular noise isparticularly loud or can be determined in an effective manner, and canrestrict the acoustic image or the evaluation range of the latter tothis smaller time range and can use this time range to evaluate the wearanalysis.

1. A method for monitoring a system, which comprises the steps of:recording and comparing a plurality of acoustic images at definedintervals of time over a period of time extending several weeks, theacoustic images each contain a plurality of acoustic image areas whichare disposed in a spatially different manner, and, between respectiverecordings of the acoustic image areas of an acoustic image, an acousticsensor is aligned with an image section, which is to be recorded, of anext image area by being moved.
 2. The method according to claim 1,which further comprises pivoting the acoustic sensor in order to bealigned with the next image area.
 3. The method according to claim 1,which further comprises providing the acoustic sensor as a directionalmicrophone for recording spatial image areas.
 4. The method according toclaim 1, which further comprises matching an outline of the acousticimage to an outline of an area, which is to be monitored, of the system.5. The method according to claim 1, which further comprises examiningthe acoustic image areas for a temporary influence.
 6. The methodaccording to claim 1, which further comprises setting a scanning rate ofthe acoustic image areas to be different.
 7. The method according toclaim 1, which further comprises comparing the acoustic image areas ofthe acoustic image with one another.
 8. The method according to claim 1,which further comprises fastening the acoustic sensor to a person, andthe acoustic image areas are recorded during activities performed by theperson in order to operate the system.
 9. The method according to claim8, which further comprises synchronizing recordings on a basis of acharacteristic of the person.
 10. The method according to claim 9, whichfurther comprises triggering a recording synchronization by an inputfrom the person.
 11. The method according to claim 9, which furthercomprises trigging a recording synchronization due to the personoperating the system.
 12. An apparatus for monitoring a system, theapparatus comprising: an acoustic sensor; a process unit for controllinga recording of a plurality of acoustic images and performing acomparison of the acoustic images at defined intervals of time over aperiod of time extending several weeks; and a movement device for movingsaid acoustic sensor, the acoustic images each containing a plurality ofacoustic image areas which are disposed in a spatially different manner,and said process unit being intended to control a movement of saidacoustic sensor between respective recordings of the acoustic imageareas of an acoustic image such that the acoustic sensor is aligned withan image section, which is to be recorded, of a next image area.